1. Field of the Invention
This invention concerns a method for reducing the cloud point and the hazing characteristics of a hydrodewaxed base stock. More particularly, it relates to a method of lowering the cloud point (particularly the overnight cloud point) of a base stock by treating same with a sulfurizing agent, either alone or in the presence of an oil-soluble magnesium, calcium or barium compound or a combination thereof, and adding a cloud point reducing amount of the sulfurized base stock to the untreated base stock. It will be understood that the method is applicable to reducing the cloud and the hazing characteristics, or the two in the alternative.
2. Discussion of the Prior Art
Many hydrodewaxed base oils have relatively high cloud points. While other properties are excellent and the cloud point appears to have no deleterious effect on the performance of formulated oils, nevertheless there are specification tests for many oils that require that there be no overnight cloud formation in the base oil at a given temperature.
The high cloud point (or overnight cloud point, ONC) is common to many hydrodewaxed oils. Much processing work, such as selective removal of the haze components and use of crystallization inhibitors, has been done with limited success. Generally, solutions to the haze formation are uneconomic or impractical because the solutions introduce other problems such as lower viscosity index, water emulsification tendency, poorer oxidation response, and the like.
While it is known to use phosphorus- and sulfur-containing compounds as additives to oils, no prior art is known that teaches or suggests that useful results can be obtained by reacting a mineral oil base stock with sulfur and compounding an additive amount thereof with an unreacted base stock. While the exact nature of the compounds formed by sulfurization leading to large improvement is not known, it is believed that various sulfide, disulfide and polysulfide linkages are formed which interface with the wax crystal growth.
Sulfurizing mineral oils is an old art. Such sulfurization is used to stabilize the oils against oxidation and to provide antiwear activity.